With the advent of one-piece and cordless telephones, the ringer signal, which alerts the recipient to the existence of an incoming call, and which was formerly produced in a base unit of the telephone has had to be produced in the telephone handset. For one-piece telephones, of course, the ringer signal must come from the handset because there is no base unit; for cordless telephones, the ringer signal must come from the handset because the base unit may be hundreds of feet away. In order to enable a person at some distance from the handset to hear the ringer, telephone manufacturers have amplified the ringer signal so that its volume is quite high. Although this poses no problem for persons who are far from the handset, it may be uncomfortable at very close range. Furthermore, if an incoming call arrives just as someone is lifting the handset to his or her ear to make an outgoing call, and if the hookswitch has not yet been moved from on-hook to off-hook (terms described below), the ringer signal volume at the ear could be excessive.
It is known that the human ear incorporates a physiological mechanism, at least for the inner ear, to protect it from loud sounds. This mechanism, which operates much like the automatic gain control (AGC) of a radio receiver, is a muscle which reduces the amount of sound that is allowed to proceed beyond the middle ear and which is controlled by nerves of the inner ear. However, the mechanism requires a short time, approximately 15 to 25 ms, before it can fully react, making it ineffective against sharp sounds such as gun shots, jackhammers, etc.